Reproducer for electric phonographs



March 3, 1942. L, D, NORTON 2,275,309

REPRODUCER FOR ELECTRIC PHONOGRAPHS Filed Aug. 5, 1940 INVENTOR LelandD. Il/orion $1 Mag 1M0 v ATTOR Patented 3, 1942 i REPRODUCER FORELECTRIC PHONOGRAPHS Leland D. Norton, Bridgeport, Conn.,-

assignor to Dictaphone Corporation, New York, 'N. Y., a corporation ofNew York Application August 3, 1940, Serial No. 350,568 2 Claims. (01.119-10041) This invention relates to electric phonographs, dictatingmachines, and the like, and more particularly to such machines of thetranscribing type and to reproducers for use with such machines.

One difficulty frequently operation of electric sound reproducingmachines is that the sound reproducing or pickup unit, in addition topicking up the sound from the record groove, also picks up considerablenoise,

encountered the stylus 26, is encased in a supporting arm 28 which i inturn is suitably mounted on the carriage III by means of a gimbal-typepivot'structure, generally usually termed hum, from stray electricalfields in the neighborhood of the machine. Such stray electrical fieldsare frequently developed by the apparatus customarily used in electricphonographs, such as driving motors, power transformers, choke coils,and other electromagnetic devices, and these stray fields areparticularly disadvantageous when the electrical phonograph is operatedfrom an A. C. power supply.

It is an object of this invention to provide an electrical reproducerfor use in electric phonographs in which the deleterious efiect of strayelectric fields is minimized or eliminated.

It is a further obiectof this invention to provide means adapted tocooperate with electric re-' producers to overcome the effects of strayfields, and thereby to eliminate undesirable noise efiects in the outputof the phonograph.

These and other apparent objects and advantages of this invention areobtained by the'means described in the following specification and maybe more readily understood by reference to the accompanying drawing, inwhich:

Figure 1 is a side elevation, partly in section, of a portion of anelectric phonograph including an electromagnetic reproducer unit;

Figure 2 is a plan view of the electromagnetic reproducer unit shown inFigure 1, taken on line 2-2;

Figure 3is a side elevation, partly insection, of a portion of an,electric phonograph showing another embodiment of the invention; and

Figure 4 shows schematicaly suitable electrical connections for theapparatus shown in Figures 1 and 2. v

The phonographic machine, shown in Figures 1 and 2 for the purpose ofillustrating the invention, is a transcribing machine having a carriage10 mounted on guide rods l2 and I4 supported on frames l6 and I8,respectively, attached to a base 20. A mandrel 22, adapted to support asound record blank 24, is suitably rotatably mounted above the baseparallel to the guide rods l2 and H. An electromagnetic reproducerindicated at 2 9.-

The pivot structure 28 may be of any suitable type which permits motionof the reproducer unit toward and away from the record 24 by rotation ofthe arm 28 about a substantially horizontal axis 30, and one whichfurther permits limited rotation in a horizontal plane about asubstantially vertical axis 32 to permit the stylus 26 freely to trackthe record sound groove when the machine is conditioned for reproducing.This I pivotal mounting structure 29 may also be provided with anarrangement to limit the oscilla tory motion about the vertical axis 32during those periods when the machine is not conditioned forreproducing. Suitable apparatus for accomplishing all of these functionsis illustrated in U. S. Patent 2,152,440 to Leland D. Norton and is notfurther described herein, because this apparatus per se does not form aportion of the present invention.

unit. generally indicated at 25, having a vibratory a. spring tween thefeed screw-34 The reproducer support arm 28 is provided with acounterweight 2'! mounted on the other side of the pivotal axis 38 fromthe reproducer 25 to partially counterbalance the pressure exerted onthe record 25 by the stylus 26 due to the weight of the reproducer 25alone.

manually operable lever 42 is provided for temporarily disengaging thefeed nut 36 'from the feed screw 38 and for lifting the stylus" from thesurface of the record 24 when it is desired to move the reproducer25 tosome other portion of the record.

Thereproducer unit 25 may be any suitable I sound translating device,such, for example, as

that shown in the co-pendingapplication Serial No. 263,229 filed byLeland D. Norton. As mayv be more easily seen in the enlarged sectionshown in Figure 2, this device comprises a C-shaped magnetic circuitstructure M in which the tips 40, supplies the driving connection be andthe carriage In. A

of the c form the pole tips 48 of the magnet. Two pickup coils 48surround the pole tips 46 and a resilient armature supportingmember 50supports an armature member 52 carrying the stylus 26 between the poletips 46, substantially as shown. It is to be understood that thiselectromagnetic reproducer device does not per se form a portion of thepresent invention, and might be any suitable reproducer unit havingoperating coils corresponding to the coils 48.

In a phonograph instrument of the type just described, the drivingmotor, amplifier transformers, chokes, etc., are frequently mounted inthe proximity of the electromagnetic reproducer 25, usually beneath thebase 20. Thus the pickup coils 48 of the reproducer 25 usually are cutby stray fields from these elements andthus transient voltages aredeveloped in these coils.

These transient voltages, as well as the sound signals developed. by thereproducer unit, are amplified and produce undesirable noises in theoutput of the phonograph. When the apparatus is operated on an A. C.power supply, the stray field is usually a 60-cycle field or theequivalent,- so that the transient voltages developed in the pickupcoils 48 by this stray field usually manivided with means for moving thecombined recorder-reproducer unit, generally indicated at 60, which isprovided with a recording stylus 62 and a reproducing stylus 64,into'either its recording or reproducing positions by means of a lever85 associated with the carriage l0 and the carriage guide I 4. The dualpurpose electromagnetic translating device 60, which is provided withonly one pickup coil 68, is mounted on one end of a lever secured to thecarriage III by means of a suitable pivotal arrangement 29, in themanfest themselves as a -cycle hum in the output of the phonograph.

In accordance with the present invention, in order to counteract thisstray field effect and eliminate the hum from the phonograph output, acompensating coil is provided, mounted near the pickup coil of thereproducer. This coil is given electrical characteristics similar tothose of the pickup coil of the reproducer, it isconnected oppositely inseries with the pickup coil, and it is mounted as close to thereproducer pickup coil as possible and is moved therewith so as to besubject to substantially the same stray field efi'ects. Thus, theparasitic voltages developed in this compensating coil due to the strayfields, are substantially equal and opposite to the voltages produced bythe stray fields in the pickup coil. If the particular electromagnetictranslating unit being used is provided with more than one pickup coil,then a plurality of compensating coils may be used, if desired, each onecorresponding to a particular pickup coil of the translating device. Inaccordance with the preferred embodiment of the present invention, a.compensating coil is provided for each pickup coil in the reproducerunit, and this compensating coil is given electrical characteristicssubstantially the same as those oiits corresponding pickup coil. Eachcompensating coil is mounted as closely as possible to its correspondingpickup coil, and it preferably lies in the plane of its pickup coil withits axis parallel to the axis of the pickup coil. However, it ispositioned so that its winding runs in the opposite direction to thewinding of the pickup coil, and it is connected in series with thepickup coil.

In the present embodiment of the invention, as shown in Figure 2, thereproducer unit 25 is provided with two pickup coils 48, and twocompensating coils 54 are mounted on a bracket 55 extending rearwardlyfrom the frame supporting the magnetic structure 44. These coils 54 areconnected in an opposed manner in series with the pickup coils 48, asshown in Figure 4.

With this arrangement, the parasitic voltages developed in the pickupcoils 48 due to stray fields are canceled out because equal and opponerabove described. However, in this embodiment a compensating coil I2,having electrical characteristics similar to those of the pickup coil68, is positioned on the lever II on the other side of the pivotal axis30 from the translating unit to in approximately the same plane aspickup coil 68 and with its axis approximately parallel to that ofpickup coil 88. With this arrangement, the compensating coil 12 not onlyis eifective in eliminating the hum picked up by the pickup coil 68,but, in addition, the weight of this coil 12 is used as a counterweightto counterbalance the weight of the translating device 68 to effectivelyreplace the counterweight 2'! shown in Figure 1.

As many possible embodiments may be made of the above invention withoutdeparting from the scope thereof, it is to be understood that all mat-'site voltages are developed in the corresponding ter herein set forthor shown in the accompanying drawing is to be interpreted asillustrative and not in a limiting sense.

I claim:

1. In an electric phonograph adapted for use with cylindrical records ofthe "hill and dale type, the combination or, a base plate, a mandrelmounted above and parallel to said base plate and adapted to support anddrive a cylindrical record surface, a carriage guide rod mounted abovesaid base plate and parallel to the axis of said mandrel, a carriagemember slidably mounted on said guide rod and adapted to be movedlongitudinally along said mandrel, a support member pivotally mounted onsaid carriage member for movement about an axis parallel to the axis ofsaid mandrel, an electromagnetic translating device having an operatingcoil and adapted to coact with a hill and dale" type record groovemounted on one end of said support lever for movement toward and awayfrom a record surface on said mandrel, and a hum compensating coilmounted on the other end of said support lever on the opposite side ofits pivotal mounting from said sound translating device and atapproximately the same distance above said base plate as the operatingcoil of said translating device whereby said compensating coil partiallycounterbalances the weight of said translating device while traveling inthe same direction with said translating device along said recordsurface in a path parallel to the axis of said mandrel and always atapproximately the same distance as the operating coil of saidtranslating device from sources of stray electric fields beneath saidbase plate.

2. In an electric sound reproducing machine aa' maoa adapted toreproduce cylindrical wax records of aroma-record on said mandrel, and ahum com I the hill and dale" type, the combination of, af' base, acylindrical mandrel mounted above and: v

with its axis parallel to said base and designed to support and drive acylindrical record, carriage guide rods mounted above said base parallelto the axis of said mandrel, a carriage slidably mounted on said guiderods, means moving said support lever for movement toward and away 5perisating coil mounted on the other end 01' said pickup support leveron the opposite side of its pivotal mounting from said picku with itsaxis a parallel to the axis of said pickup coil and at apcoil partiallycounterbalances the Weight of saidpickup while traveling in the samedirection with said pickup along said record in a path parallel to saidbase and the axis of said mandrel and always at approximately thesame'distance as the pickup from sources of stray electric fields be-

